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Disorders of bone mineralisation Flashcards

1
Q

What are the signs and symptoms of hypercalcaemia?

A
  • Asymptomatic
  • Bones
    • excessive bone resorption
  • Stones
    • renal
    • polyuria/polydipisa, dehdyration, kidney stones
  • Groans
    • intestinal
    • constipation, anorexia, nausea and vomiting
  • Psychic moans
    • cns
    • confusion/ stupor
  • other symptoms- stiff joints/myopathy/hypertension
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2
Q

Describe the causes of hypercalcaemia?

A
  • Primary hyperparathyroidism
  • Malignancy
  • Familial
    • Multiple endocrine neoplasia ( MEN) I & II
      • ​MEN 1- pancreatic/pituitary tumours
      • Men 2- thyroid medullary caricinoma of thyroid and bilateral phaeochromoctyomas
    • familal hypocalciuric hypercalcaemia
      • ​defect in calcium-sensing receptor -> poor renal clearance
  • Endocrine
    • Hyperthyroidisim
    • Addison’s disease
  • Exogenous
    • Vitamin D excess
    • steriod admininstration
  • Metabolic
    • milk alkali syndrome
  • Granulomas
    • sarcoidosis - generating 1,25 (OH)2 D3
  • Tertiary hyperparathryroidism
    • ​after prolonged primary hyperparathyroidism, where the glands act autonomously secreting excess PTH-> hypercalcaemia
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3
Q

What is the aetiology of primary hyperparathyroidism?

A
  • Solitary parathyroid adenoma 80%
  • parathyroid hyperplasia 15%
  • Multiple parathyroid adenomas 4%
  • parathyroid carcinoma 1%
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4
Q

What is seen in primary hyperparathyroidism?

A
  • Plasma calcium high
  • Plasma phosphate is low ( increased renal excretion)
  • -> bone reabsorption & inadequate repair ( lack of phosphate)
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5
Q

What is seen on ecg with primary hyperparathyroidism?

A
  • Decreased QT interval
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6
Q

What is the blood/urine picture of primary hyperparathyroidism?

A
  • High calcium
  • High PTH
  • Low phosphate

Urine

  • high phosphate
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7
Q

What is seen on xrays with primary hyperparathyroidism?

A
  • osteopenia
  • predilection for cortical bone
  • osteitis fibrosa/ brown tumours
  • subperiosteal resorption
    • radial borders of proximal phalanges and tufts of distal phalanges
  • Pepper pot skull
  • chondrocalcinosis and metastatic calcification in soft tissues
  • loss of lamina dura around teeth is specific
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8
Q

What tumours cause hypercalcaemia?

A
  • Those that secrete PTH- related protein
  • esp Squamous lung carcinoma
  • solid tunours with bony mets
    • ​breast, kidney, thyroid , prostate
    • cytokine related effects IL1, IL6 and TNF-alpha via activation of osteoclasts
  • Haematological malignancues
    • clonal plasma cell resorb bone in mutliple myeloma via cytokine related effects
    • lymphomas synthesise 1,25 (OH)2 D3
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9
Q

What is the tx of hypercalcaemia?

A
  • tx underlying cause
  • rehydration with normal saline ( saline diuresis)
  • Loop diuretics with or without dialysis ( severe cases)
  • Specific pharmacotherapy
  • Bisphosphonates
  • Chemotherapy in malignancy e.g. Mithramycin
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10
Q

What are the symptoms of hypocalcaemia?

A
  • Neuromuscular irritability
    • Tetany
    • seizures
    • Chvostek’s sign
      • tapping over parotid gland in region of facial nerve -> muscle twitches
    • Trosseau’s sign
      • carpopedal spasm if brachial artery occluded with blood- pressure cuff
    • Depression
    • ECG- prolonged QT
  • ​Chronic
    • Cateracts
    • Fungal nail infections
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11
Q

What are the aetiology of hypocalcaemia?

A

Low PTH and low vitamin D => hypocalcaemia

  • Hypoparathyroidism
  • Pseudo-hypoparathyroidism
  • Renal osteodystrophy
  • Osteomalacia/Rickets
  • Hypophosphatasia
  • Oncogenic osteomalacia
    • non ossifying fibroma
    • neurofibromatosis
    • fibrous dysplasia
    • haemangiopericytomas
  • Anticonvulsant medication- phenytoin
  • high does bisphosphonates
  • heavy metal over dose
  • chronic alcoholism
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12
Q

What are the causes of hypoparathyroidism?

A
  • Usually post surgery- thyroidectomy
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13
Q

What are the effects on blood test in hypoparathyroidism?

A
  • Decreased PTH-> low plasma Calcium
  • High plasma phosphate
  • Alkaline phosphatase normal
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14
Q

What are the symptoms of hypoparathyroidism?

A
  • Those for hypocalcaemia
    • tetany
    • seziures
    • chvostek’s and trosseay sign
    • depression
    • longer QT interval
  • Vitalgo and hair loss
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15
Q

What is the tx of hypoparathyroidism?

A
  • Vitamin D analogues e.g. alfracalcidol
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16
Q

What is the aetiology of peusdo- hypoparathyroidism?

A
  • Rare inherited disorder due to failure of target cells response to PTH
  • pathology due to
    • PTH receptor abnormality
    • Signalling abnormality e.g. cyclic AMP defect, G protein abnormality
    • Lack of necessary cofactors e.g. magnesium
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17
Q

Name one type of pseudo- hypoparathyroidism?

A
  • Albright hereditary osteodystrophy
    • BORESS
      Brachyldactyly- short 1st.4th/5th MT and MC
    • Obesity
    • Reduced Intelligence
    • exostoses
    • Skull xray show basal ganglia calcification
    • subcutaneous ossification
18
Q

what are the effects of pseudo-hypoparathyroidism/

A
  • Increased PTH ( can produce it but target cells don’t respond to it)
  • Low calcium
  • Normal or increased Alkaline phosphatase
19
Q

What is renal osteodystrophy?

A
  • A group of disorders of bone mineral metabolism seen in chronic renal failure
  • High turnover renal bone disease
  • low turnover renal bone disease
20
Q

what is seen in high turnover renal bone disease?

A
  • uraemia
  • phosphate retention
21
Q

how does high turnover renal bone disease lead to hypocalcaemia?

A
  • high plasma phosphate ->
    • impaire synthesis of 1,25 (OH)2 vitamin D3 by inhibiting renal 1-alpha hydroxylase ( note that synthesis of renal vitamin D metabolite is also directly impaired by tubular damage in renal failure)
    • direct lowering of calcium which stimulates PTH
    • direct stimulation of PTH secretion
  • Low serum calcium -> secondary Hyperparathyroidism and ultimately hyperplasia of the chief cells of the parathyroid gland and tertiary hyperparathyroidism
  • as renal function deteroriates acidosis exacerbates the negative calcium balance
22
Q

What is seen in low turnover renla bone disease?

A
  • Slowed bone formation and turnover- adynamic response
  • Slowed mineralisation- osteomalacia
  • Alumium deposits
    • impaired renal excretion
    • inhibtion of proliferation and differentiation of Osteoblasts
    • Inhibition of PTH release from pararthyroid gland
  • No secondary hyperparathyroidism
23
Q

what are the effects of renal osteodystrophy?

A
  • Hypocalaemia
    • rickets/osteomalacia
  • SUFE
  • Secondary hyperparathyroidism
    • osteitis fibrosa et cystica ( bone marrow replacement by fibrous tissue)
    • osteosclerosis (20% cases)
      • from 2ary hyperparathyrodism
      • increased OB activity
      • lucent and dense bands in spine- rugger-jersey spine
    • metastatic calcification
      • ca and phosphate solubility may be affected -> ectopic calcifications in the conjuctivia, blood vessels, skin and periacrticular vessels
  • Amyloidosis
    • as a result of beta-1 microglobulin from chronic diaylsis
    • clinical effects= pathological fx ( amyloid deposits) arthropathy, carpal tunnel syndrome
    • dx made on histology woth Congo red stain
24
Q

What are the laboratory changes in renal osteodystrophy?

A
  • Increased urea and creatinine
  • Increased phosphate
  • Low/ normal calcium
  • raised alkaline phosphatase ( osteoblasts)
  • High PTH ( low calcium stim/ direct stim of PTH)
25
Q

How is the dx of renal osteodystrophy made?

A
  • Tetracycline labelled bone biopsy
26
Q

What is the tx of renal osteodystrophy?

A
  • Mainly medical
  • adjust serum phosphate to normal
    • reduce dietary intake ( less eggs/milk/cheese)
    • Phosphate binders - calcium carbonate
  • Adjust calcium to normal
    • Increase calcium absorption with 1,25 (OH)2 D3
    • Calcium supplementation
  • Supress secondary hyperparathryroidism
    • 1,25 (OH)2 D3 or may reiquire parathyroidectomy
  • Chleate bone aluminium in cases of aluminium retention ( with desferrioxamine)
  • Manage chronic renal failure with dialysis of renal transplant
27
Q

Define osteomalacia?

A
  • Is a deficient or impaired mineralisation of the bone matrix
28
Q

What is Rickets?

A
  • Is the juvenile form of osteomalacia with impaired mineralisation of cartilage matrix ( chondroid) affecting the physis in the zone of provisional calcification
29
Q

what is the aetiology of rickets/osteomalacia?

A
  1. Dietary deficiency
    • Calcium or vitamin D deficiency
    • Dietary chelators ( phytates in chapattis, oxalates in spinach)
    • Phosphorous deficiency ( aluminium containing antacid abuse)
  2. Gastrointestinal malabsorption
    • post- gastrectomy
    • biliary disease
    • intestinal defects
    • short bowel syndrome, coeliac disease, crohn’s disease
  3. Renal tubular defects ( loss of phosphate)
    • hypophosphataemic vitamin d resistant rickets
    • mutliple renal tubular defects-> aminoaciduria ( fanconi syndrome)
    • Renal tubular acidosis
  4. Hereditary vitamin D dependent rickets
  5. Hypophosphatasia
  6. Oncongenic osteomalacia
    1. ​fibrous dysplasia, non ossifiying fibroma
  7. ​anticonvulsants- phenytoin
  8. high dose bisphosphonates
  9. heavy metal overdose
  10. chronic alcoholism
30
Q

what is hypophosphataemic vitamin D resistant rickets/osteomalacia?

A
  • Most common form of rickets
  • **X linked dominant **
    • mutation in P-EX gene
  • Impaired renal tubular reabsorption of phosphate
  • charactertistic deformity
    • bilateral symmetrical anterolateral femoral and tibial bowing​
  • ​normal GFR but reduced vitamin D response
  • xrays resemble anklosing spondylitis with ligamentous calfication and ossification ( enthesiopathy)
31
Q

what is the tx of hypophosphataemic vitamin D resistant rickets/osteomalacia?

A
  • Phosphate replacement
  • high does vitamin D3 necessary
32
Q

What is the inherited form of multiple renal tubular defects-> aminoaciduria?

A
  • Cystinosis
33
Q

What is the acquired form of mutliple renal tubular defects-> aminoaciduria?

A
  • mutliple myeloma
34
Q

What is renal tubular acidosis?

A
  • proximal ( bicarbonate wasting)
  • distal ( H+ gradient effect)
  • acquired- ureterosigmoid anastomosis
35
Q

What is hereditary vitamin D -Dependent rickets?

A
  • V rare
  • clinically severe rickets with alopecia totalis, epidermal cysts and oligodontia ( missing 5 or more adult teeth)
  • inherited defect of 25 (OH)2 vitamin D3 hydroxylation
36
Q

what is the difference between type 1 and type 2 hereditary vitamin D -Dependent rickets?

A
  • Type 1
    • renal 1 alpha hydroxylasse deficiency
    • autosomal recessive
    • chromosome 12q14
  • Type 2
    • end organ insensitivity to 1,25 (OH)2 vitamin D3
    • abnormality in nuclear receptor
37
Q

What is hypophosphatasia?

A
  • Autosomal recessive disorder of phosphate synthesis
  • due to low levels of alkaline phosphatase
  • increased urine phosphoethanolamine is diagnostic
  • trend towards distinguishing hypophosphatasia as a clinical entitiy separate from osteomalacia
38
Q

What is generally seen in rickets?

A
  • Retarded bone growth and short stature
  • Pathological fx
    • Looser’s zones on compression side ( see image)
  • symptoms of hypocalcaemia
  • Proximal myopathy
    • vitamin D receptors present in skeletal muscle
39
Q

What is seen in rickets looking head to toe?

A
  • Delayed Frontal closure and frontal parietal bossing
  • Dental disease
  • enlarged of costochondral junction - rachitic rosary
  • Harrison sulcus - indentation of lower ribs at diaphragm insertion
  • centrally depressed ‘cod fish vertebra’ dorsal kyphosis ( cat back)
  • bowing of knees - sabre shin
  • waddling gait
40
Q

What is seen on bloods from a child with rickets?

A
  • Increased PTH
  • Low Calcium
  • Low phosphate
  • Low vitamin D levels
41
Q

What is seen on xrays of rickets?

A
  • Physeal increase in height and width- continues to growth but can’t mineralise
  • metaphyseal cupping, flaring and jagged appearance
  • small ossified nuclei
  • coxa vara
  • flattening of skull
42
Q

What is seen on plain xrays of osteomalacia?

A
  • Looser’s zones- stress fx on concave border of long bones
  • Milkman pseudo-fx on compressio side of long bones ( fx healed but not mineralised)
  • biconcave vertebral bodies -> severe kyphosis
  • thin cortices, indistinct, fuzzy trabeculae
  • triradiate pelvis
  • signs of hyperparathyroidism

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